1. Field of the Invention
Aspects of the present invention relate to a flat panel display using a signal transmission method of transmitting a differential signal, and more particularly to a flat panel display that includes a differential signaling system for impedance matching that uses the signal transmission method.
2. Description of the Related Art
In general, a cathode ray tube (CRT) is one of widely used display devices. The CRT has been used in a monitor for televisions, measuring instruments, or information terminals. Since the CRT is heavy and large, the CRT cannot keep up with recent requirements for small and light-weight devices.
Accordingly, as a substitute for the CRT, various flat panel displays such as liquid crystal displays (LCD), plasma display panels (PDP), field emission displays (FED), and organic light emitting displays (OLED) have been studied and developed which have advantages in view of small, compact, light-weight, and low electric power consumption requirements. The above described flat panel displays include various components, and wirings to transmit signals between the various components.
Recently, with the development of electronic circuit and manufacturing process technology, signals can be transmitted through the wirings at high speeds. To meet such high speed signal transmission requirements, drive speeds of the components have become high. Accordingly, various methods of transmitting signals between the components through wirings have been suggested. For example, a signal transmission method such as a low voltage differential signal (LVDS) method or a reduced swing differential signaling (RSDS) method of transmitting a differential signal has been used.
A differential signaling system transmits a different mode signal having the same amplitude and a different polarity through a differential transmission line. Accordingly, there is a tendency in the differential signaling system to remove a concentrated magnetic field and to couple an electric field. A high speed signal can be stably transmitted without a signal reflection and a skew (phase delay) electro magnetic interference (EMI) due to the coupled electric field.
A related art flat panel display will be described in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing a structure of a related art flat panel display. With reference to FIG. 1, the related art flat panel display includes a display panel 40, a gate driver 20, a data driver 30, and a controller 10. Pixels (not shown) are arranged on the display panel 40 in a matrix pattern. The gate driver 20 sequentially applies a scan signal to gate wirings of the display panel 40. The data driver 30 applies an image signal DATA1 to data wirings of the display panel 40. The controller 10 applies the image signal DATA1 from an external graphic controller (not shown) to the data driver 30, and applies a control signal CS1 to the gate driver 20 and the data driver 30 in order to control drive timing. In the related art flat panel display, after all the gate wirings of the display panel 40 are sequentially scanned and the image signal DATA1 is applied to the pixels through the data wirings to display one frame of an image, a vertical synchronous signal VSYNC is applied to display a next frame of the image.
FIG. 2 is a block diagram showing in detail a controller and a data driver shown in FIG. 1. FIG. 3 is a view showing a signal transmission method used between the controller and the data driver. With reference to FIG. 2, the data driver 130 is composed of a plurality of data driving circuits 132. The plurality of data driving circuits 132 receive image signals DATA [+,−] from the controller 110 through first and second wirings W1 and W2, and receive a control signal CS11 from the controller 110 through a third wiring W3.
The data driver 130 includes a plurality of data driving circuits 132 therein. The data driving circuits 132 receive the image signals DATA [+,−] from the controller 110, and output the image signals DATA [+,−] to the data wirings according to the control signal CS11 from the controller 110. Although not shown in drawings in detail, a plurality of data wirings are electrically coupled to the data driving circuits 132, and apply the image signals DATA [+,−] applied to the data driving circuits 132 to the pixels.
The image signals DATA [+,−] from the controller 110 are transmitted to the respective data driving circuits 132 using the aforementioned differential signal transmission method. Namely, as shown in FIG. 3, in order to transmit one data group of the image signals DATA [+,−], a differential transmission line arrangement is provided. Namely, first and second wirings W1 and W2 are provided between the controller 110, being a sending end Tx, and the data driving circuit 132, being a receiving end Rx.
On the other hand, a termination resistor Rt is installed between differential transmission lines of the receiving end Rx (data driving circuit 132) side. The termination resistor Rt electrically connects the first wiring W1 and the second wiring W2 to each other, which are connected to each data driving circuit 132. Accordingly, an image signal DATA [+] that is applied through the first wiring W1 is transferred to the controller 110 by way of the termination resistor Rt and the second wiring W2. The termination resistor Rt prevents an excessive current from flowing into the data driving circuit 132. A voltage across the termination resistor Rt is the image signals DATA [+,−], which is applied to the data driving circuit 132.
A plurality of electric devices and wirings are provided in the flat panel display, and are electrically coupled to each other. Since the electric devices and wirings have an impedance component, the impedance component generates an attenuation of a signal during the signal's transmission between the electric devices. Accordingly, the controller 110 and the data driving circuits 132 have an impedance component. Further, the first and second wirings W1 and W2 to connect the controller 110 and the data driving circuits 132 have an impedance component Z0.
If the impedance value Z0 of the first and second wirings W1 and W2 is different from that of the data driving circuits 132, namely, when an impedance mismatching occurs, the image signals DATA[+,−] are not exactly supplied to the data driving circuits 132. That is, a part of the image signals DATA [+,−] is reflected and discharged.
In detail, a reflection coefficient Γ caused by the impedance mismatch is expressed by a following equation 1.
                    Γ        =                                            Z              diff                        -                          R              t                                                          Z              diff                        +                          R              t                                                          (        1        )            
where, a differential impedance Zdiff is a value that is less than a sum (2Z0) of impedance values of the first and second wirings (W1, W2), and has a different value depending on variations in a manufacturing process and construction of the flat panel display.
According to equation (1), when the differential impedance Zdiff is identical with a value of the termination resistor Rt, a reflection loss of a signal does not occur. However, the differential impedance Zdiff varies in practice. Accordingly, in the related art, impedance matching is not normally achieved in the differential transmission method.
When a reflection wave occurs due to impedance mismatching, an interference with the image signals DATA [+,−] applied through the first wiring W1 occurs to cause unstable waves, signal distortions, and signal attenuations. The electro magnetic interference (EMI) also deteriorates image quality of the flat panel display.